A technique is developed to predict the dynamic contact forces arising after passing road surface irregularities by a vehicle modeled as an undamped multiple-degrees-of-freedom (MDOF) system. An MDOF system moving along an uneven profile is decomposed into an aggregate of independent oscillators in the modal space, such that the response of each oscillator can be calculated independently. The technique developed is applied to the calculation of the coefficients of the harmonic components of the contact forces arising after the passage of a "cosine" pothole. The application of the technique to other problems is also discussed. One interesting phenomenon reported in the DIVINE project , regarding the replacement of a steel suspension by an air suspension resulted in increase of the maximum response of short-span bridges is explained by applying the technique suggested. The discussion is amply illustrated by examples of the application of the technique to the calculation of the tire forces due to a pothole for two simple - quarter-car and half-car - vehicle models.